Doctor, Should I Take Vitamins?

Vitamin A

Two potential forms of Vitamin A exist in nature. Vitamin A as retinol is only found in animal products and supplements. Carotenoids (like beta-carotene) are present in fruits and vegetables and are converted by our bodies into vitamin A.

Vitamin A's association with several types of cancer and cardiovascular disease has been studied extensively and is summarized below:

Breast Cancer: The Nurses' Health Study suggests that a high intake of carotenoids may reduce the risk of breast cancer, especially in premenopausal women at increased risk for breast cancer. However, the Iowa Women's Health Study found no association between dietary vitamin A and breast cancer.

Lung Cancer: Two large, randomized, placebo-controlled studies searched for a connection between beta-carotene and lung cancer among men at an increased risk for this type of cancer. Both studies showed increases in lung cancer risk among men who took antioxidant supplements.

Prostate Cancer: The ATBC Cancer Prevention Study found that cancer deaths increased with the use of beta-carotene supplementation.

Colorectal Adenoma (pre-cancer): A four year study of antioxidant supplementation revealed no reduction in the development of adenoma risk in more than 800 people randomized to receive either beta-carotene, vitamin C and E, or all three together.

All Cancers: The Physicians Health Study found that 12 years of beta-carotene supplements had no effect on the occurrence of cancer. Over 7000 women studied in the Women's Antioxidant Cardiovascular Study found that, after more than 9 years, beta-carotene supplements had no effect on the incidence of cancer. The ATBC Cancer Prevention Study showed that cancer deaths increased with the use of beta-carotene supplementation.

Heart Disease: Studies of vitamin A and beta-carotene have not found a reduction in the incidence of coronary artery disease. In one study the risks were increased.

Immune System Function: An improvement in immune function has been found after vitamin A therapy in malnourished, vitamin A deficient people. No improvement in immune function is clear in healthy people who add vitamin A to their diets.

Bone Fractures: Vitamin A is clearly associated with an increase in the number of bone fractures and osteoporosis in the elderly. Physicians routinely caution women at high risk for osteoporosis not to take vitamin A or retinol supplements.

Diseases of the Eye: Macular degeneration is a disease of the retina that slowly steals vision. Studies show that antioxidants do not prevent or slow the progression of mild macular degeneration but may reduce the risk of progression in moderate or advanced cases of this disease. Beta-carotene, Vitamin A and Vitamin C are typically considered in these cases. Vitamin E is generally avoided due to its increased risk of heart failure and death from all causes.

Vitamin A Recommendation:

Vitamin A supplementation in otherwise healthy individuals is discouraged because of its lack of proven benefit and the possible adverse effects it has related to cancer and cardiovascular disease.